1. Field of the Invention
The present invention relates to numerical controllers for controlling machine tools and the like, and more particularly to a numerical controller provided with the function of preventing mutual interference of movable parts of a machine tool and the like.
2. Description of Related Art
A numerical controller for controlling a machine tool controls the operation of movable parts (control axes) of the machine tool in accordance with an NC program created beforehand, to machine a workpiece to be machined.
While the workpiece is machined by the machine tool, the respective parts of the machine tool, such as a tool, tables, a workpiece-clamping jig and a spindle table, must not interfere with one another. To prevent such interference, interference check has conventionally been performed to determine whether or not the respective parts of the machine tool and the workpiece interfere with one another.
For example, a technique has been known in which each machine part that may possibly cause interference, such as a tool, is defined as an interference object by using a combination of solid bodies, and the created definition is stored in memory. A current position of the interference object is obtained, and the position of the interference object after movement of the axis is obtained by interpolating move commands. Then, a region in which the solid body constituting the interference object can cause interference during the movement of the interference object from the position before the interpolation to the position after the interpolation is calculated as an interference decision solid, and an interference decision region is set using a combination of such interference decision solids, to allow interference to be checked based on the set interference decision region (cf. JP 09-230918A).
In the above technique of checking interference on the basis of the interference decision region, the interference checking process is executed after the interpolation process is performed by the numerical controller. With this technique, however, if the interference checking process is prolonged due to increase in the number of objects of interference check (e.g., tools, tool holders, workpieces, jigs, and tables) and the number of solid bodies constituting the objects, the interpolation process of the numerical controller fails to be executed quickly and thus slows down, causing the interference checking process to be interrupted in the middle.